Process for controlled sub-micron dispersions in alloys



June 30, 1970 J.'A.'ALEXANDER 3,513,

PROCESS FOR CONTROLLED SUB-MICRON DISPERSIONS IN ALLOYS Filed 001;; 27, 1966 dire/191 7 7mperazure Comparisop of .Sfrengf/z vs. fempe/aure for disperszorz strengthened and h0m09enou5 afloys INVENTOR, Jbhn QQ/exanaer BY 22/ /1414 w Maul ATTORNEYS.

United States Patent Oflice 3,518,106 Patented June 30, 1970 3,518,106 PROCESS FOR CONTROLLED SUB-MICRON DISPERSIONS IN ALLOYS John A. Alexander, Oxon Hill, Md., assignor to the United States of America as represented by the Secretary of the Army Filed Oct. 27, 1966, Ser. No. 590,102 Int. Cl. 844d 1/14 US. Cl. 117-71 2 Claims ABSTRACT OF THE DISCLOSURE An alloy having high structural strength suitable for use in such high temperature applications as gas turbine equipment, which is produced by vacuum deposition of dispersions of sub-micron particles of a dissimilar metal on a thin heated layer of a matrix metal, oxidation of the dispersions of particles, overlaying the oxidized 'dispersions with a second thin layer of the matrix metal, and repeating the process of depositing dispersions of submicron particles oxidized and covered with a layer of matrix metal to produce a three dimensional alloy structure of matrix metal with dispersions of sub-micron particles of a dissimilar metal distributed in the matrix metal.

The invention described herein may be manufactured and used by or for the Government, for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to the controlled dispersion of dissimilar metal particles in a matrix metal in such a manner as to substantially improve the structural properties of the resultant alloy.

Heretofore, techniques for accomplishing dispersions of particles in a metal matrix include precipitation at a low temperature from a super-saturated solid solution, by eutectoid decomposition and by mechanical mixing of powders. The first two of these techniques are diffusion processes and thus the size and distribution of particles is subject to change during elevated temperature exposure. Dissolution or agglomeration of particles by diffusion is detrimental to the elevated temperature properties of these types of alloys. The third process incorporates stable particles in the metal matrix by mechanical mixing. The

size and uniformity of spacing of such mixtures is dependent upon availability of micron size particles and the ability of the fabricator to accomplish homogeneous mixtures. At least two techniques for the accomplishment of more controlled particle size and distribution exist in the SAP and TD type powders. SAP dispersion alloys are formed by pressing metal powders such as aluminum which have been surface oxidized. TD type dispersion alloys typically involve the colloidal codispersion of thorium OXide and nickel oxide followed by the reduction of the nickel oxide.

Each of the above described state of the art processes are limited by elevated temperature instability, relatively coarse particle size, non-uniform distribution or relatively large interparticle spacing.

It is therefore the object of this invention to overcome these disadvantages by attaining a uniform dispersion of a very fine temperature stable phase in the desired matrix with small interparticle spacing.

This objective is achieved by the treatment of this process which consists in depositing a thin film of the intended matrix metal of controlled thickness by vacuum deposition; subsequently a dissimilar metal which can be preferentially oxidized is vacuum deposited in a quantity sufficient to initiate the formation of isolated islands on the thin film substrate; the island deposit can be characterized as having an average island diameter and an inter-island distance or spacing; the island diameter and the inter-island distance can be controlled by variations in the substrate temperature, the rate of deposition and the time of deposition. The planner :dispersion created in this manner is preferentially oxidized by simple exposure to oxygen at elevated temperature or by anodization techniques. The oxidized planar dispersion is then overlayed by a second layer of the matrix metal of equal thickness and this dispersion of the intermediate layer provides a thermodynamically stable second phase. The treatment heretofore outlined is repeated and this results in the construction of a three dimensional distribution of dispersed second phase particles in the matrix metal. This treatment permits complete control over the particle size in the submicron range and over interparticle spacing on the same sub-micron scale.

Experimentally the process was carried out by depositing aluminum islands on a gold substrate with the aluminum being oxidized to aluminum oxide. This process is also applicable to the formation of stable oxide, carbide, nitride, boride, phosphide or silicide particles in structural metals such as nickel, chromium, cobalt, titanium, columbium, tantalum, molybdenum, tungsten, aluminum, magnesium, iron and copper.

The drawing is a schematic illustration of strength versus temperature curve for a conventional metallic alloy as compared with a dispersion strengthened alloy. The dispersion strengthened materials are advantageous for the design of equipment for elevated temperature because their strengths are maintained relatively constant over a broad temperature range as indicated in the drawing. The shaded area indicates the temperature range over which a dispersion strengthened alloy can be expected to excel in design for the elevated temperature application.

There are many advantages in having such materials available for more severe temperature environments and as a practical application this improvement becomes particularly important in the increased efliciencies which re sult from being able to design and operate gas turbine equipment at higher temperatures.

Thus, the essence of this treatment for the formation of alloys, is that it alfords a means of controlling the size of the islands and their spacing which is utilized to miniaturize these dimensions for improvement in the structural qualities of the laminated product.

What is claimed is:

1. A process for the production of sub-micron size dispersions in metals or alloys comprising, depositing in a vacuum on a heated matrix metal a. dissimilar metal from a vapor for the formation of closely spaced sub-micron size islands, oxidizing the metal islands for the formation of a planar dispersion of particles, overlaying the oxidized planar dispersion with a layer of the matrix metal, and repeating these steps to form a three dimensional alloy structure of matrix metal with oxidized dispersions of submicron particles of a dissimilar metal distributed therethrough, said alloy structure having high structural strength suitable for sustained use in high temperature applications.

2. The process of claim 1 in which the matrix layers comprise films of gold and the islands comprise aluminum which is oxidized to form aluminum oxide.

References Cited UNITED STATES PATENTS 3,261,720 7/1966 McCormack 117-107 X 3,368,919 2/1968 Casale et all. 117-212 X ALFRED L. LEAVITT, Primary Examiner C. K. WEIFFENBACH, Assistant Examiner U.S. Cl. X.R. 117-107 

